The below should ensure that VECTOR_DIAG cannot be disabled on targets
that have guaranteed vector support, such as the SH MPC target. However,
I can disable the option without getting any complaints, even though 
the option to check for valid config after each change was set.







        cdl_component CYGSEM_HAL_VIRTUAL_VECTOR_SUPPORT {
            display     "Enable use of virtual vector calling interface"
            active_if   CYGINT_HAL_VIRTUAL_VECTOR_SUPPORT
            requires    { (0 ==
CYGINT_HAL_VIRTUAL_VECTOR_SUPPORT_GUARANTEED) ||
CYGSEM_HAL_VIRTUAL_VECTOR_DIAG }
            calculated  1
            description "
                Virtual vector support allows the HAL to let the ROM
                monitor handle certain operations. The virtual vector table
                defines a calling interface between applications running in
                RAM and the ROM monitor."
            compile     hal_if.c hal_misc.c
            
            cdl_option CYGSEM_HAL_VIRTUAL_VECTOR_DIAG {
                display       "Do diagnostic IO via virtual vector table"
                default_value {
CYGINT_HAL_VIRTUAL_VECTOR_SUPPORT_GUARANTEED }
                description   "
                    All HAL IO happens via the virtual vector table / comm
                    tables on targets that guarantee that service. On
                    other targets, it can be optionally enabled if the
                    ROM monitor is known to have virtual vectors - note
                    that output may disappear if the ROM monitor does not
                    provided the necessary services and this option is
                    enabled. When it is not enabled (on older targets)
                    the IO is always done using functions compiled into
                    the application image."
            }